1. Field of the Invention
The present invention relates to an automatic running control system for vehicles, particularly to a running control system for a car having an automatic transmission and an automatic cruising control in which transmission control and automatic cruising control can be integrally carried out, while a locked clutch is compusorily operated when the automatic cruising is instructed during a predetermined level of car speed, for instance, more than 60 km/h (37.3 mile/h) and the locked up condition of an automatic transmission is maintained.
2. Description of the Prior Art
Generally, in a car with an automatic transmission function and an automatic cruising function, it is constructed in such a manner that one control unit for gear transmission control and another control unit for automatic cruising control are provided in order to independently perform the gear transmission control and the automatic cruising control. In this case, while a predetermined lock-up pattern is prepared in advance for the transmission control unit as lock-up arises, a decision is made as to whether or not the lock-up clutch, i.e. the clutch for mechanically coupling the input shaft to the output shaft of a torque converter, should be operated.
In this case, as a close relationship exists between the lock-up function and the automatic cruising function described above, the maintaining of the lock-up condition during, for instance, the automatic cruising, enables the power transmission efficiency to improve and this, in turn, enables also the fuel consumption to improve. Moreover, in this case when performing the automatic cruise control in the lock-up condition, it is also possible to improve the response thereof and to carry out an accurate vehicle speed control, while a sufficient and preferable engine brake is obtainable at a descending slope.